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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

GLACIERS OF HAKRIMAN FIORD AND PORT WELLS          341
GLACIAL EROSION
Glacial Erosion above Sea LevelóGeneral. The evidence of intense glacial erosion in Harriman Fiord, Barry Arm, and Port Wells, is plainly visible above sea level and clearly indicated by soundings. Throughout the fiords, glacial striae, conforming in direction to the different trends of the fiords, and roches moutonnees are present upon bare rock ledges near sea level, being especially well shown in the barren zones. These features prove clearly that ancestors of the present glaciers completely occupied the fiords, and suggest the probability that the fiords were given their present straight courses, simple outlines, and steepened lower slopes by ice erosion without sinking of the land.
The extreme height of glaciation in Harriman Fiord and Port Wells was estimated by Gilbert to be 4000 feet or more, on the basis of the "cordon of high hanging valleys" surrounding Harriman Fiord. "Above Barry, Serpentine and Surprise glaciers they contain hanging glaciers at a general height of about 4000 feet, and east of Harriman Glacier their ice banks coalesce in a continuous terrace along the valley wall. The surface of the trunk glacier to which they are adjusted probably lay 5000 feet above present sea level."
The evidence from sea level indicates that the 2900 foot hill back of Pt. Doran was completely overridden, for the summit and slopes are rounded, and the cliffs are all of such small size as might readily be made by glacial plucking or by post-glacial weathering. The same is true of the summit of Esther Island east of Port Wells. There is a general rounded appearance to all the bare summits throughout Harriman Fiord and Port Wells below 5000 feet, except near the present glaciers where there are many cirques separated by narrow aretes and sharpened peaks. -
Plucking and Oversteepening. Some of the lower slopes have been steepened to precipices. There are many illustrations of steepened slopes in Harriman Fiord and Barry Arm. Oversteepening of the lower slopes of the fiord wall between Baker and Detached Glaciers recently caused a great avalanche.
Because of the steepness of the slopes and the consequent absence of soil, many areas of bare rock on the fiord walls are as yet without vegetation excepting in joints and hollows. This condition is well illustrated on the south shore of the inlet leading to Surprise Glacier where the roches moutonnees, glacial grooves, and striae are still well preserved. Many of the beautiful waterfalls in Harriman Fiord and Barry Arm, as along the coast between Pt. Doran and Toboggan Glacier, cascade down bare rock slopes made smooth by glacial erosion. The bare knob at the extreme southeastern limit of the barren zone on the eastern side of Barry Arm shows the roches moutonnees form very well indeed.
Asymetrical Fiord Watts. Pt. Doran is a gently sloping spur which contrasts with the much oversteepened opposite slope below Mt. Curtis, because the united Barry-Harriman Fiord Glacier flowed faster and eroded more efficiently on the eastern side of this curve. That it did not fail to erode the hill behind Pt. Doran also is proved by the fact that all rock ledges not covered with soil or moss are rounded knobs with striae and grooves, a good example of which is seen in the great, overhanging glacial groove shown in PI. CXXXVHI.
The eastern and western sides of Port Wells form a striking contrast, the former having a markedly oversteepened lower slope, rising up to a distinct shoulder, while the western